1. Field of the Invention
This invention relates generally to a novel data service or transmission system capable of shuffling an information data and by which an information or data service can be received by a pay system, and more particularly, is directed to a novel decoding means used in a data transmission system for decoding a control data portion the data length of which can be varied.
2. Description of the Prior Art
As a prior art data transmission system which can provide a particular information to only a particular subscriber, there is known one which uses a special network line.
To be more concrete, the particular information transmitted from the data base station by using a special network line is received by a decoder located at the side of a subscriber and the subscriber can receive the information at the station side.
By the way, the above mentioned data transmission system has such a defect that when the number of subscribers is increased considerably, it becomes difficult to secure the special network line.
When the information supplied by the station side are such as stock information, commodity exchange information in a plurality of markets and so on which require a lot of money to collect the information and supply it to the information transmitting facilities thereof, it is necessary to creat a system that those who are not the subscribers can not decode the data with ease. Since according to the prior art data transmission system, the information can be easily obtained by the provision of a decoder at a subscriber, those who are not the subscriber can easily obtain the information.
Although in such case a highly-sophisticated wiretap preventing means must be provided, the prior art data transmission system does not employ any such means.
In the prior art, if the subscriber purchases the decoder once, so long as the subscriber holds such decoder, the subscriber can always receive the information. However, when the cost for collecting the information and the facility expenses for managing the station amount to a large sum, it is preferable that the information is supplied with a charge.
However, such data transmission system is not yet developed at present, in which a large number of subscribers are intended, the information can be shuffled with high secrecy and the information can be supplied with a charge.